The present invention relates to a tunable laser source device, particularly to a tunable laser source device having a tunable laser source of an external resonance type that varies the wavelength of emitted light by changing the resonator length of the external resonator by driving a driver such as a motor, the above tunable laser source device employing a technology capable of sweeping the wavelength of the emitted light at a high speed and capable of outputting the accurate information of the wavelength to be swept.
Generally in many cases, the measurement of optical characteristics by an optical device is performed by a measurement system, in which the emitted light from the tunable laser source device capable of varying the wavelength is input to a device under test (DUT) and various kinds of the optical characteristics of the DUT are measured based on the change of the output light from the DUT with respect to the wavelength of the input light.
FIG. 9 schematically shows the constitution of the prior art as the optical characteristics measuring system for such an optical device.
That is, in the optical characteristics measuring system for the optical device, for example, the input light whose wavelength is variable to a DUT 100 such as an optical band-path filter is input to a tunable laser source device 201 constituting an optical transmitter 200 via an optical transmission path 101 such as an optical fiber.
The output light from the DUT 100 is output to, for example, an optical characteristics measuring device 301 such as an optical spectrum analyzer constituting an optical receiver 300 via an optical transmission path 102 such as the optical fiber.
Then, in the optical characteristics measuring device 301, as described later, various kinds of the optical characteristics, for example, band-pass characteristics of the optical band-path filter are measured based on the change of the output light from the DUT 100 with respect to the wavelength of the input light by performing data processing in a data processor, after an electric signal which is obtained by photoelectric conversion at a light receiving unit is sampled in a sampling unit.
In this case, wavelength information of the input light necessary for each processing of the optical characteristics measuring device 301 on the side of the optical receiver 300, for example, a tunable start wavelength, an stop wavelength, a tunable range and the like, are transmitted by the so-called CPU communication from a CPU 202 included in a controller on the side of the optical transmitter 200 to a CPU 302 included in the controller on the side of the optical receiver 300.
FIG. 10 is a block diagram exemplifying a concrete constitution of a controller 130 on the side of the optical transmitter 200 used in the foregoing measurement system and a tunable laser source 121 of the external resonance type which can be controlled by the controller 130.
Here, the tunable laser source 121 of the external resonance type is constituted so as to vary the wavelength of an omitted light by changing the resonator length of the resonator constituted of a diffraction grating 1c rotatively driven by a motor 123 as the driver, an optical lens 1b and a laser diode (LD) 1a. 
It is to be noted that a stepping motor is used as the motor 123 herein.
Wavelength information input means 131 in the controller 130 is used to input information for determining a point wavelength for measurement including a start wavelength xcexs and a stop wavelength xcexe for sweep by, for example, key operation.
Further, point information measurement means 132 in the controller 130 stores and sets, as point information, in a point information memory 133, a step number m of the motor 123 corresponding to each point wavelength including the start wavelength xcexs and the stop wavelength xcexe for the sweep, based on the information input from the wavelength information input means 131 and the information stored in a memory table 133.
Furthermore, in the memory table 133 in the controller 130, for example, a state where the emitted wavelength of the tunable laser source 121 is longest is set as a reference, and wavelengths xcex(0), xcex(1) . . . xcex(N) in the case that the entire tunable wavelength range is indicated by a predetermined unit wavelength (for example, 0.01 nm) and the step numbers 0, 1 . . . N of the motor 123 corresponding to these wavelengths are stored in advance.
Furthermore, in the case where the start wavelength xcexs and the stop wavelength xcexe for the sweep and a point number M are input from, for example, the wavelength information input means 131, the point information setting means 133 in the controller 130 obtains a wavelength distance xcex94xcex by dividing a difference between the start wavelength xcexs and the stop wavelength xcexe by a number smaller than the point number M by 1, and then obtains the point wavelengths of M pieces, xcexp(1)=xcexs, xcexp(2)=xcexs+xcex94xcex, xcexp(3)=xcexs+2xcex94xcex, . . . xcexp(Mxe2x88x921)=xcexexe2x88x92xcex94xcex, xcexp(M)=xcexe.
Then, this point information setting means 33 selects the step numbers m(1), m(2) . . . m(M) which correspond to these point wavelengths, respectively, from the memory table 133, and stores and sets in the point information memory 134.
It is to be noted that, in the case that the wave distance xcex94xcex is designated instead of the stop wavelength xcexe, the point wavelengths of M pieces, xcexp(1)=xcexs, xcexp(2)=xcexs+xcex94xcex, xcexp(3)=xcexs+2xcex94xcex, . . . xcexp(Mxe2x88x921)=xcexs+(Mxe2x88x922)xcex94xcex, xcexp(M)=xcexs+(Mxe2x88x921)xcex94xcex=xcexe are obtained, and the step numbers m(1), m(2) . . . m(M) which correspond to these point wavelengths are stored and set in the point information memory 134.
Further, when drive control means 135 in the controller 130 receives a start instruction of measurement from an operation unit or the like not shown, it obtains the step number m(1) corresponding to the start wavelength xcexs from the point information memory 134.
Then, the drive control means 135 outputs an up-pulse to positively rotate the motor 123, if the obtained m(1) is positive.
Alternatively, the drive control means 135 outputs a down-pulse to reversal rotate the motor 123, if the obtained m(1) is negative.
Then, the drive control means 135 initially sets the emitted wavelength to one step before the start wavelength xcexs, and thereafter, sweeps the wavelength of the emitted light in a range of from the start wavelength xcexs to the stop wavelength xcexe by continuously outputting the up-pulse for positively rotating the motor 23 by a number equal to a difference m(M)xe2x88x92m(1) between the step number m(1) corresponding to the start wavelength xcexs and the step number m(M) corresponding to the stop wavelength xcexe.
Here, the drive control means 135 gradually shortens a pulse frequency from the initial period of the drive until reaching a predetermined speed, and gradually lengthens the pulse frequency from the predetermined speed until stopping, in order to control the motor 123 in a trapezoid.
Further, a driver 136 in the controller 130 supplies the up-pulse and the down-pulse output from the drive control means 135 to the motor 123, thereby driving the motor 123 in steps.
Furthermore, sweep signal output means 141 in the controller 130 is constituted of voltage data generation means 141a, a voltage data memory 141b, voltage data reading means 141b an a D/A converter 141d. 
Here, among the point wavelengths xcexp(1), xcexp(1) . . . xcexp(M) determined by the information input from the wavelength information input means 131, the voltage data generation means 141a generates a predetermined sweep starting voltage Vs (for example, 0V) for the start wavelength xcexs=pxcex(1), a predetermined sweep ending voltage Vet (for example, 10V) for the stop wavelength xcexe=xcexp(M), and a voltage data of V(I)=(ixe2x88x921)xc3x97(Vsxe2x88x92Vs)/(Mxe2x88x921) for point wavelengths xcexp(1) (i=2, 3 . . . Mxe2x88x921) between them in the case that a distance between the point wavelengths is constant, and then, the same means 141a stores and sets the voltage data in the voltage data memory 141b. 
It is to be noted that the voltage data generation means 141a obtains the point wavelength from the information input from the wavelength information input means 131, and generates the voltage data utilizing the point wavelength obtained by the foregoing point information setting means 132.
Further, the voltage data reading means 141c sequentially reads out the voltage data V(1), v(2) . . . V(m) from the voltage data memory 141b to set them in the D/A converter 141c. 
Accordingly, the voltage monotonically changes from the D/A converter 141d so as to be a value corresponding to the emitted wavelength, that is, a sweep signal is output in which the voltage rises by (Vsxe2x88x92Vs)/(Mxe2x88x921) every time the emitted wavelength matches each point wavelength.
As described above, the tunable laser source device used on the side of the optical transmitter 200 in the optical characteristics measuring system of such an optical device is constituted of the laser source 121 of the external resonance type that varies the emitted wavelength by changing the resonator length of the external resonator which is constituted of a laser diode 1a, a diffraction grating 1c for diffracting the emitted light of this laser diode 1a and an optical lens 1b, and the controller 130 that controls the motor 123 of this laser source 121 to output the light of a desired wavelength from the laser source 121.
The controller 130 on the side of this optical transmitter 200 previously stores a relation between the wavelength of the emitted light and rotation positional information of the diffraction grating 1c which ca be varied by the motor 123, and stops the diffraction grating 1c at the rotation position corresponding to the point wavelength designated to be measured, and then transmits a signal (wavelength information) which shows reaching the point wavelength to the side of the optical transmitter 300 by the CPU communication as described above, whereby the sampling and the like of the data can be performed on the side of the optical transmitter 300.
However, in the measurement system using in this way the tunable laser source device that stops the movement of the diffraction grating 1c every time the designated point wavelength is reached, when there are a number of point wavelengths, for example, as in a case where the band-pass characteristics and the like of the optical band-path filter are measured, activation and stopping of the motor 123 must be repeated every time all the point wavelengths.
Particularly, in the case of the stepping motor generally used as the motor 123, the activation and stopping need to be performed at an extremely low speed in order to rotate accurately by a slight amount of angle.
Thus, when such slow activation and stopping are subjected to the stepping motor at every point wavelength, a time of from an initial point wavelength to the last point wavelength becomes extremely long. Moreover, since the wavelength information at every time needs to be transmitted each time from the side of the optical transmitter 200 to the side of the optical transmitter 300 by the aforesaid CPU communication, there has existed a problem that a time required for the measurement as the entire measurement system became extremely long.
An object of the present invention is to provide a tunable laser source device, particularly a tunable laser source device having a tunable laser source of an external resonance type that varies the wavelength of an emitted light by driving a driver such as a motor to change the resonator length of an external resonator, whereby the wavelength of the emitted light can continuously or intermittently be varied at a high speed in a range of from a previously set start wavelength to stop wavelength so that a high speed measurement can be performed even in the case where it is applied to an optical characteristics measuring system of an optical device having a number of the point wavelengths, and accurate wavelength information of the wavelength varied continuously or intermittently at a high speed can be output.
According to the present invention, to achieve the foregoing object, there is provided:
(1) a tunable laser source device having a tunable laser source (21) in which a wavelength of emitted light is continuously or intermittently varied from a start wavelength to a stop wavelength that are previously set, by varying, with a driver (23), a resonator length of an external resonator which is constituted including a laser diode (24) and a diffraction grating (26), the tunable laser source device comprising:
point wavelength information setting means (32) for setting point wavelength information representing positional information about the driver, which corresponds to each resonator length of the external resonator regarding the start wavelength and the stop wavelength of the light emitted from the tunable laser source and a plurality of wavelengths obtained by dividing a range between the start wavelength and the stop wavelength into arbitrary steps;
drive control means (35) for controlling the driver to continuously or intermittently vary the wavelength of the light emitted from the tunable laser source, in the range of from the start wavelength to the stop wavelength;
emitted wavelength information detecting means (37) for detecting emitted wavelength information corresponding to the wavelength of the light emitted from the tunable laser source, which is continuously or intermittently varied by the drive control means in the range of from the start wavelength to the stop wavelength;
matching determination means (38) for determining whether the emitted wavelength information detected by the emitted wavelength information detecting means matches each point wavelength information set by the point wavelength information setting means; and
information output means (40), (41) for receiving an output from the matching determination means and for outputting predetermined information to an outside when the emitted wavelength information matches each point wavelength information.
In addition, according to the present invention, to achieve the foregoing object, there is provided:
(2) the tunable laser source device described in (1), in which the information output means comprises timing information output means (40) for receiving an output of the matching determination means and for outputting, as the predetermined information, to the outside, timing information representing a time when the emitted wavelength information matched each point information.
Further, according to the present invention, to achieve the foregoing object, there is provided:
(3) the tunable laser source device described in (1), in which the information output means comprises sweep signal output means (41) for receiving an output of the matching determination means and for outputting, as the predetermined information, to the outside, a sweep signal that monotonically varies to change a voltage at a time the emitted wavelength information matched the point information, to a value corresponding to the wavelength of the emitted light.
Further, according to the present invention, to achieve the foregoing object, there is provided:
(4) the tunable laser source device described in (1), in which the information output means comprises:
timing information output means (40) for receiving an output of the matching determination means and for outputting, as the predetermined information, to the outside, timing information representing a time when the emitted wavelength information matched each point information; and
sweep signal output means (41) for receiving an output of the matching determination means and for outputting, as the predetermined information, to the outside, a sweep signal that monotonically varies to change a voltage at a time the emitted wavelength information matched the point information, to a value corresponding to the wavelength of the emitted light.
Furthermore, according to the present invention, to achieve the foregoing object, there is provided:
(5) the tunable laser source device described in (1), in which the emitted wavelength information detecting means comprises a counter (37) for counting an output of the drive control means.
Still further, according to the present invention, to achieve the foregoing object, there is provided:
(6) the tunable laser source device described in (1), in which the emitted wavelength information detecting means comprises a counter (37) for counting an output corresponding to the positional information about the driver.
Still further, according to the present invention, to achieve the foregoing object, there is provided:
(7) the tunable laser source device described in (1), in which the emitted wavelength information detecting means detects the emitted wavelength information based on an output corresponding to the positional information about the driver.
Furthermore, according to the present invention, to achieve the foregoing object, there is provided:
(8) the tunable laser source device described in (1), in which the emitted wavelength information detecting means detects the emitted wavelength information based on an output corresponding to the wavelength of the light emitted from the tunable laser source.